From the beginning of man's enjoyment of recorded music, efforts have been continually made to improve the quality of reproduction of the recorded sounds. Improvements have been made in the means for producing recorded sounds, for amplifying the recorded signal, and for playing back the recorded signals into a listening area. The loudspeakers used for music playback serve as but one example of the continuing effort to produce improved, high fidelity sound.
Loudspeaker designs have been developed over the years to address a variety of shortcomings in the reproduction process. One problem in obtaining faithful reproduction of an audio input signal is attributable to the varying energies of the output audio waves from the loudspeaker. Low frequency waves propagated from an acoustic source such as a loudspeaker are quickly dispersed in the listening area as the wave moves from the acoustic source. Such waves are described as non-directional. Higher frequency waves of from about 250 Hz to the upper range of human audibility do not disperse as readily as they leave the acoustic source. The waves, which are propagated in a specific direction, tend to maintain that direction for a longer period of time than the low frequency waves. Thus, the higher frequency waves are described as directional, the effect being known generally as the beaming effect.
A person standing directly in front of a loudspeaker acoustic source generating a wide band of frequency waves will be able to perceive the full frequency output. That same person, standing off to one side of the loudspeaker acoustic source, would perceive more of the low frequency waves than of the high frequency waves because of the dispersal properties of the low frequency waves. A person standing directly in front of a loudspeaker acoustic source is said to listen to the audio output "on axis". A person standing to the side of the loudspeaker acoustic source perceives the audio signal "off axis".
One is able to enjoy the maximum frequency response of the loudspeaker acoustic source by positioning oneself close to the "on axis" line of the loudspeaker. Unfortunately, movement away from the axis decreases one's enjoyment of full frequency response output.